Conventionally, parking assistance devices that assist a parking operation of a driver performing garage parking of a vehicle have been used. JP 2009-206615A discloses an example of this type of technique.
The parking assistance device disclosed in JP2009-206615A is configured to, while a vehicle travels along a direction in which a road extends, detect an entrance portion of a parking space into which the vehicle is about to be parked, and calculate a guide route for the vehicle based on the detection result. If white lines have been drawn on only the left and right sides of the parking space, the parking assistance device detects the front end portions of the pair of white lines and sets the entrance portion to be on a straight line connecting the two front end portions of the white lines. Also, if the parking space is completely surrounded by white lines, the parking assistance device sets the entrance portion of the parking space to be on the white line drawn in the vehicle width direction that is on the frontmost side of the parking space. Furthermore, if other vehicles have already been parked on the left and right sides of the parking space in which the vehicle is about to be parked, the parking assistance device recognizes the front corner portions of the vehicles and sets the entrance portion to be on a line connecting the two front corner portions.